Late-season insects could hit Kentucky corn crop

Cool temperatures, coupled with periods of rain, have kept much of Kentucky’s corn out of the ground.

As producers hustle to compensate for lost planting time, they should be aware that late-planted corn could present a different insect scenario this year.

The good news is the state's late-planted corn is not likely to see increased problems with corn rootworm and is likely to see reduced wireworm damage. However, several pests do not arrive until later in the season, and these pests could pose the greatest threat to yields.

"Late-planted corn means late-harvested corn," said Ric Bessin, Extension entomologist in the University of Kentucky College of Agriculture. "Therefore, the crop could be more susceptible to late-arriving pests like black cutworm or late-season pests, such as fall armyworm and the second generation of southwestern and European corn borers."

Corn borers usually appear in two different generations throughout the growing season in Kentucky. Corn planted after May 10 is more likely to see damage from the second generation, which arrives in late-July to early-August. The second generation of corn borers will attack corn that is near or just completed tasseling by tunneling into the stalk causing it to weaken.

"Growers should try to control corn borers with insecticides while they are on the outside of the plant," Bessin said. "Insecticides will not control them once they tunnel into the stalk."

To protect against southwest and European corn borers, growers can plant Bt varieties with resistance to the insects. Those who cannot use Bt varieties should scout their fields periodically for pests and use insecticides to control both types of corn borers when they appear on the crop.

Black cutworms also could pose a threat to late-planted corn. Black cutworms attack young seedlings between 12 and 18 inches tall by cutting stalks at the soil line and feeding on the plants' leaves. They favor moist soils and wet conditions during the spring. The greatest potential for damage from black cutworms occurs between planting and mid-June.

Another pest that could pose a threat to late-planted corn is the fall armyworm. Bessin said state fall armyworm populations were small in past years, but the pest is more likely to infest late-planted corn. Corn planted after June 1 that is still in the whorl stage in July and August has the greatest threat of a fall armyworm infestation. Like corn borer control, timing is critical to controlling fall armyworm populations. Growers should treat crops with insecticides when they see larva on corn leaves.

Fall armyworm larva is very difficult to control if it is allowed to tunnel into the whorl and make a frass plug. The frass plug allows the larva to feed on the plant and creates a barrier that prevents insecticides from controlling the pest.